1. Field of the Invention
The present invention relates generally to a mechanical seal device with an improved sealing ability and an easy installation of a shaft sleeve. More particularly, the invention relates to a mechanical seal device which retains a relative pressure difference in fluid pressure of a sealed fluid chamber, an intermediate chamber and a buffer fluid chamber to enhance its sealing ability.
2. Description of the Related Art
There has been a mechanical seal device as a relative art of the present invention, as shown in FIG. 3. FIG. 3 shows a half sectional view of the shaft seal device.
In FIG. 3, a shaft seal device 100 is disposed between the inner diameter surface of a housing 160 and the outer diameter surface of a rotary shaft 150. This shaft seal device is a tandemly configured mechanical seal device. This tandem type mechanical seal device comprises a contacting type mechanical seal device 101 in the region of sealed process fluid and a non-contact type mechanical seal device disposed in the atmospheric region.
In the contacting type mechanical face seal 101, a rotary seal ring 102 and a stationary seal ring 103 are disposed adjacent and opposite to each other. The rotary seal ring 102 and the stationary seal ring 103 make a sealing contact at respective sealing faces 104 and 105 wherein the rotary seal ring 102 is fixedly connected to one of split parts comprising a second shaft sleeve 141 and the mating stationary seal ring 103 is fixedly connected to a second seal cover 131. The sealing faces 104, 105 are elastically pressed against each other by springs 107 which are disposed on the back face 106 of the stationary seal ring 103. In addition, the pressure exerted on the back face 106 by the sealed process fluid pushes the sealing face 104 against the sealing face 105. An O-ring 108 is disposed on the inside diameter surface of the stationary seal ring 103 which determines the pressure area of the back face 106.
In the non-contact type mechanical seal device 110, a second rotary seal ring 111 and a second stationary seal ring 115 make a sealing contact at a second sealing face with spiral grooves 113 and a second sealing face 112, respectively. Contact between the second sealing face with spiral grooves 113 and the second sealing face 112 is further reinforced by a spring 116 and the pressure of purge gas exerted on a back face 117 of the stationary seal ring 115. The pressure area of the back face 117 is determined by an O-ring 119 which is disposed in the inner annular groove of the back face 117. The second stationary seal ring 115 is axially movable relative to a first seal cover 132 so that the second sealing face 112 is sufficiently biased by the spring 116 against the second sealing face with spiral grooves 113.
The rotary seal ring 111 fits over a first shaft sleeve 140 and is retained between a third shaft sleeve 142 and the mating part of the split parts of the second sleeve 141.
The flange of the first sleeve 140 engages a step of a rotary shaft 150. The first sleeve 140 fixates the second sleeve 141 and the second rotary seal ring by means of the third sleeve 142. Furthermore, a lock nut 143 engages a screw thread 144 prepared on the rotary shaft 150 so as to prevent the first sleeve 140 and the third sleeve 142 from moving in an axial direction. These three sleeves, 140, 141, 142, are separated parts and five O-rings 146 are installed for the sake of sealing
A seal cover fixedly connected to the housing 160 is comprised of a first seal cover 131 and a second seal cover 132. The seal covers 131 and 132 are fixedly held between a step of the housing 160 and a presser cover 133. The seal covers 131 and 132 have a passage 121 to feed a purge gas into an intermediate chamber C′. Pressure of the purge gas is set lower than the pressure of the sealed process fluid.
The shaft seal device 100 constructed accordingly has to be able to retain the primary seal ring 102 and the secondary seal ring 111 so that they are free to rotate. Therefore, it is not only that the first, the second, and the third sleeves 140, 141, 142 become large in size, but that they have to be separable. Being separable parts then necessitates as many as five O-rings 146. This in turn yields a mass increase of the first, the second and the third sleeves, which requires a large diameter of the rotary shaft 150 to assure a high speed rotating motion. In addition, the tandem configuration of the mechanical seal device leads to a large axial length.
Since the pressure of the intermediate chamber C′ is lower than the pressure of the sealed process fluid, there may be a leakage of the sealed process fluid into the intermediate chamber. Also the mechanical seal device 110 residing in the atmospheric region is a non-contact type, therefore the purge gas may leak to the atmospheric region. Accordingly, there remain problems in the seal performance of the shaft seal device 100.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to collect the sealed process fluid with no leakage to the atmospheric region by enhancing the seal performance of the seal parts against the atmosphere region.
Another goal is to collect all the leaking fluid into the intermediate chamber without further leaking to the atmospheric region by means of the pressure of the intermediate chamber not only being set lower than the pressure of the sealed fluid but also being set lower than the pressure of the buffer fluid chamber.
Yet another goal is to fixate sleeves without use of fitting devices, to reduce the weight of the sleeves and their fitting devices, to achieve a high-speed rotating motion of the rotary shaft, and to reduce a production cost by decreasing the number of parts as the result of a weight reduction of the sleeves.